XML 116 R99.htm IDEA: XBRL DOCUMENT
v3.19.1

Derivatives (Realized and Unrealized Gains (Losses) with Respect to HFT Derivatives) (Details) - Designated as Hedging Instrument [Member] - Held for Trading Hedge [Member] - CAD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items] |  |
Gain (Loss) on Derivative Instruments Held for Trading Purposes, Net | $ 195 | $ 420
Power swaps and physical contracts [Member] | Non-regulated fuel for generation and purchased power [Member] |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Gain (Loss) on Derivative Instruments Held for Trading Purposes, Net | 2 | 2
Power swaps and physical contracts [Member] | Other Operating Income (Expense) [Member] |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Gain (Loss) on Derivative Instruments Held for Trading Purposes, Net | (12) | 7
Natural gas swaps, futures, forwards, physical contracts [Member] | Non-regulated fuel for generation and purchased power [Member] |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Gain (Loss) on Derivative Instruments Held for Trading Purposes, Net | 0 | 10
Natural gas swaps, futures, forwards, physical contracts [Member] | Other Operating Income (Expense) [Member] |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Gain (Loss) on Derivative Instruments Held for Trading Purposes, Net | $ 205 | $ 401

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_DerivativeInstrumentsGainLossLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Aggregate net gain and losses (whether realized or unrealized) on all derivative instruments held for trading purposes whether or not settled physically. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41322-113958 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4F -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624186-113959 + Details
Name: | us-gaap_GainLossOnDerivativeInstrumentsHeldForTradingPurposesNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_HedgingDesignationAxis=us-gaap_DesignatedAsHedgingInstrumentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=ema_HeldForTradingHedgeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=ema_PowerSwapsAndPhysicalContractsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IncomeStatementLocationAxis=ema_NonRegulatedFuelForGenerationAndPurchasedPowerMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IncomeStatementLocationAxis=us-gaap_OtherOperatingIncomeExpenseMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=ema_NaturalGasSwapsFuturesForwardsPhysicalContractsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |